Method and arrangement for supplying power to several induction coils in an induction apparatus

• US 7,910,865 B2
• Filed: 11/02/2007
• Issued: 03/22/2011
• Est. Priority Date: 05/04/2005
• Status: Expired due to Fees

• Current Assignee: EGO Elektro-Gerã¤Tebau GmbH (EGO Blanc und Fischer & Company GmbH)
• Original Assignee: EGO Elektro-Gerã¤Tebau GmbH (EGO Blanc und Fischer & Company GmbH)
• Inventors: Friedrich, Hartmut, Bögel, Jörg, Haag, Thomas
• Primary Examiner(s): Ralis; Stephen J
• Assistant Examiner(s): Dang; Ket D
• Application Number:
  US11/934,480
• Publication Number:
  US 20080087661A1
• Time in Patent Office: 1,236 Days
• Field of Search: 219/10.77, 219/10.49 R, 219620-627, 219661-667, 219672-676, 118/723.I, 118/723.IR, 118/724, 118/725
• US Class Current: 219/620
• CPC Class Codes: H05B 6/065 using coordinated control of multiple induction coils

Abstract

An arrangement for controlling induction coils of an induction cooking hob so as to minimize noise production resulting from intermodulation of certain frequencies of operation. The induction coils are operated in two modes, with a first mode at the same frequency f_g so to produce a low intermodulation or differential frequency, or at a second mode having a high differential frequency of about 18 kHz. Alternating back and forth between said modes of operation makes it possible to reach predefined average values for the power of the induction coils for a given time period, while at the same time minimizing development of disturbing noise.

Claims

1. A method for supplying power to a plurality of induction coils in an induction apparatus, each said induction coil having a respective frequency converter and being supplied with said power by means of said respective frequency converter operating at a given frequency, wherein during simultaneous operation of the plurality of said induction coils, said frequencies of said frequency converters are set as a function of said power provided with respect to a frequency difference between said frequencies according to one of the following operating modes:

a) said frequency difference is zero,

b) said frequency difference is less than 1 kHz, or

c) said frequency difference is between 15 kHz and 25 kHz, and

wherein at a start of operation a first induction coil and a second induction coil are operated;

a) with said first induction and said second induction coil both starting at a first common frequency and decreasing from the first common frequency to a second common frequency wherein at said second common frequency operation results in;

1) a first power provided to said first induction coil that is greater than a subsequently provided first average power provided to said first induction coil, and

2) a second power provided to said second induction coil that is less than a subsequently provided second average second power provided to said second induction coil;

b) wherein subsequent to reaching said second common frequency, said induction coils are operated;

1) during a first time period wherein said first power of said first induction coil decreases to a level less than said first average power, and said second power of said second induction coil increases to a level greater than said second average power, and

2) during a second time period wherein said first power of said first induction coil increases to a level above said first average power, and said second power of said second induction coil decreases to a level less than said second average power.

2. The method according to claim 1, wherein two induction coils are operated according to one of said aforementioned operating modes a) to c).

3. The method according to claim 1, wherein a subsequently alternating operation of said induction coils takes place with either said aforementioned common frequency for a first specific time or with said aforementioned frequency difference for a second specific time, said first specific time being equal to:

4. The method according to claim 1, wherein said frequency difference for operating mode b) is a maximum of 500 Hz.

5. The method according to claim 1, wherein said frequency difference for operating mode c) is approximately 18 kHz.

6. The method according to claim 1, wherein said plurality of induction coils are operated in a frequency range of approximately 16 kHz to 100 kHz.

7. The method according to claim 6, wherein at said start of operation said induction coils are operated with a high frequency in a mode as saucepan detection coils.

8. A system for controlling an induction hob having at least two separately controllable induction coils comprising:

a first induction coil associated with a first frequency converter capable of being supplied with a first average power level;

a second induction coil associated with a second frequency converter capable of being supplied with a second average power level;

a power source supplying said first average power level and said second average power level;

a controller controlling said first frequency converter and said second frequency converter over a first time period wherein;

a) a first frequency of said first frequency converter results in a first power level of said first frequency converter, and

b) a second frequency of said second frequency converter results in a second power level of said second frequency converter,

said controller maintaining a frequency difference between said first frequency and said second frequency such that said frequency difference during said first time period is one of;

a) less than 1 khz, or

b) between 15 kHz and 25 kHz,

wherein said controller further controls said first frequency converter and said second frequency converter over a second time period wherein;

a) a third frequency of said first frequency converter results in a third power level of said first frequency converter that is different from said first power level, and

b) a fourth frequency of said second frequency converter results in a fourth power level of said second frequency converter that is different from said second power level, wherein said second frequency difference between said third frequency and said second frequency is the other of;

a) less than 1 kHz, or

b) between 15 kHz and 25 kHz.

9. The system of claim 8 wherein said first induction coil and said second induction coil are incorporated into a single hotplate element on the induction hob.

10. The system of claim 8 wherein said controller further maintains

a) the frequency difference less than 1 kHz for the first time period, and wherein said third power level during the second time period is less than said first power level of said first time period, and

b) the frequency difference between 15 kHz and 25 kHz for the second time period and wherein said fourth power level during said second time period is higher than said second power level of said first time period.

11. The system of claim 8 wherein said first induction coil and said second induction coil are respectively incorporated into a first hotplate element and a second hotplate element on the induction hob.

12. The system of claim 11 wherein the controller produces an average power over the first time period and the second time that is equal to the desired power level.

13. The system of claim 11 wherein the controller repeats the first time period and the second time period in sequence.

14. A controller for a hob having at least two separately controllable induction coils, performing the steps of:

controlling a first frequency converter of said hob associated with a first induction coil of said hob to supply a first power level (P₁(f_g1)) to the first induction coil at a first frequency (f_g1) during a first time period (t_g);

controlling a second frequency converter of said hob associated with a second induction coil of said hob to supply a second power level (P₂(f_g2)) to the second induction coil at a second frequency (f_g2) during said first time period (t_g);

controlling the first frequency converter to supply a third power level (P₁(f_v1)) to the first induction coil at a third frequency (f_v1) during a second time period (t_v);

controlling the second frequency converter to supply a fourth power level (P₂(f₂)) to the second induction coil at a fourth frequency (f_v2) during the second time period (t_v), wherein

a difference between the first frequency (f_g1) associated with the first induction coil and the second frequency (f_g2) associated with the second induction coil during the first time period (t_g) is less than 1 kHz, and

a difference between the third frequency associated with the first induction coil (f_v1) and the fourth frequency (f_v2)associated with the second induction coil during the second time period (t_v) is between 15 kHz and 25 kHz.

15. The controller of claim 14 wherein the sum of the first power level and the second power level correspond to the sum of the third power level and the fourth power level.